Package org.rrd4j.core

Class RrdDefTemplate

  • public class RrdDefTemplate
extends XmlTemplate

    Class used to create an arbitrary number of RrdDef (RRD definition) objects from a single XML template. XML template can be supplied as an XML InputSource, XML file or XML formatted string.

    Here is an example of a properly formatted XML template with all available options in it (unwanted options can be removed):

     <rrd_def>
     <path>test.rrd</path>
     <!-- not mandatory -->
     <start>1000123456</start>
     <!-- not mandatory -->
     <step>300</step>
     <!-- at least one datasource must be supplied -->
     <datasource>
         <name>input</name>
         <type>COUNTER</type>
         <heartbeat>300</heartbeat>
         <min>0</min>
         <max>U</max>
     </datasource>
     <datasource>
         <name>temperature</name>
         <type>GAUGE</type>
         <heartbeat>400</heartbeat>
         <min>U</min>
         <max>1000</max>
     </datasource>
     <!-- at least one archive must be supplied -->
     <archive>
         <cf>AVERAGE</cf>
         <xff>0.5</xff>
         <steps>1</steps>
         <rows>600</rows>
     </archive>
     <archive>
         <cf>MAX</cf>
         <xff>0.6</xff>
         <steps>6</steps>
         <rows>7000</rows>
     </archive>
 </rrd_def>

    Notes on the template syntax:

    • There is a strong relation between the XML template syntax and the syntax of RrdDef class methods. If you are not sure what some XML tag means, check javadoc for the corresponding class.
    • starting timestamp can be supplied either as a long integer (like: 1000243567) or as an ISO formatted string (like: 2004-02-21 12:25:45)
    • whitespaces are not harmful
    • floating point values: anything that cannot be parsed will be treated as Double.NaN (like: U, unknown, 12r.23)
    • comments are allowed.

    Any template value (text between <some_tag> and </some_tag>) can be replaced with a variable of the following form: ${variable_name}. Use setVariable() methods from the base class to replace template variables with real values at runtime.

    Typical usage scenario:

    • Create your XML template and save it to a file (template.xml, for example)
    • Replace hardcoded template values with variables if you want to change them during runtime. For example, RRD path should not be hardcoded in the template - you probably want to create many different RRD files from the same XML template. For example, your XML template could start with: 
       <rrd_def>
     <path>${path}</path>
     <step>300</step>
     ...
    • In your Java code, create RrdDefTemplate object using your XML template file: 
       RrdDefTemplate t = new RrdDefTemplate(new File(template.xml));
    • Then, specify real values for template variables: 
       t.setVariable("path", "demo/test.rrd");
    • Once all template variables are set, just use the template object to create RrdDef object. This object is actually used to create Rrd4j RRD files: 
       RrdDef def = t.getRrdDef();
 RrdDb rrd = new RrdDb(def);
 rrd.close();
    You should create new RrdDefTemplate object only once for each XML template. Single template object can be reused to create as many RrdDef objects as needed, with different values specified for template variables. XML syntax check is performed only once - the first definition object gets created relatively slowly, but it will be created much faster next time.

    • Constructor Detail

      • RrdDefTemplate

        public RrdDefTemplate​(InputSource xmlInputSource)
               throws IOException
        Creates RrdDefTemplate object from any parsable XML input source. Read general information for this class to find an example of a properly formatted RrdDef XML source.
        Parameters:
        xmlInputSource - Xml input source
        Throws:
        IOException - Thrown in case of I/O error
        IllegalArgumentException - Thrown in case of XML related error (parsing error, for example)

      • RrdDefTemplate

        public RrdDefTemplate​(String xmlString)
               throws IOException
        Creates RrdDefTemplate object from the string containing XML template. Read general information for this class to see an example of a properly formatted XML source.
        Parameters:
        xmlString - String containing XML template
        Throws:
        IOException - Thrown in case of I/O error
        IllegalArgumentException - Thrown in case of XML related error (parsing error, for example)

      • RrdDefTemplate

        public RrdDefTemplate​(File xmlFile)
               throws IOException
        Creates RrdDefTemplate object from the file containing XML template. Read general information for this class to see an example of a properly formatted XML source.
        Parameters:
        xmlFile - File object representing file with XML template
        Throws:
        IOException - Thrown in case of I/O error
        IllegalArgumentException - Thrown in case of XML related error (parsing error, for example)

    • Method Detail

      • getRrdDef

        public RrdDef getRrdDef()
        Returns RrdDef object constructed from the underlying XML template. Before this method is called, values for all non-optional placeholders must be supplied. To specify placeholder values at runtime, use some of the overloaded setVariable() methods. Once this method returns, all placeholder values are preserved. To remove them all, call inherited clearValues() method explicitly.

        Returns:
        RrdDef object constructed from the underlying XML template, with all placeholders replaced with real values. This object can be passed to the constructor of the new RrdDb object.
        Throws:
        IllegalArgumentException - Thrown (in most cases) if the value for some placeholder was not supplied through setVariable() method call